The present invention relates generally to voltage isolation, and more specifically to magnetic voltage isolation techniques.
Avalanche ionization is a physical phenomenon that significantly decreases the operating voltage range of various low-pressure systems. Avalanche ionization typically occurs in low-pressure, gas-filled environments when high potential electrons collide into and break apart molecules into atoms and additional high potential electrons. The additional high potential electrons, in turn, take part in a chain reaction in which more and more molecules are broken apart. This chain reaction causes the gas to change into highly conductive plasma.
Avalanche ionization is problematic, for example, in low-pressure applications (e.g., less than 10 Torr) in which a component that is maintained at a high voltage is separated from another component, which is maintained at ground potential, by a gas-filled passageway. When avalanche ionization occurs within the gas-filled chamber, the created plasma forms an electrical pathway between the separated components, which drains the voltage from the high-voltage component. The plasma effectively short circuits the components and prevents high-voltage operation.
Exemplary applications of low-pressure applications include semiconductor fabrication systems, electron microscopes, and space-based ion propulsion systems. In semiconductor fabrication systems, the wafer and the chuck holding the wafer are maintained at very high voltages, typically in the range of thousands of volts, and a connected vacuum pump is at ground potential. In electron microscopes, the microscope is maintained at a high voltage and a connected vacuum pump is at ground potential. In the case of an ion engine, an ion source, typically maintained at a high voltage, is connected to a gas-feed system at ground potential. In each type of system, it is desirable to prevent avalanche conditions by increasing the threshold voltage at which plasma ionization occurs.
Currently, approaches for preventing avalanche ionization have been implemented. However, these techniques have certain drawbacks that leave the industry wanting for a more superior method. For instance, one current technique involves separating the high voltage source and the nearest ground by a large distance. This technique is impractical, however, because the necessary distances are typically infeasible in light of physical space limitations. Another technique involves separating the high voltage component and the grounded component by forming part of the gas chamber that connects the components with an electrically insulating material. Unfortunately, this technique is simply not very effective in reducing the breakdown threshold voltage. Yet another technique involves placing a porous dielectric material in the line between the high voltage component and the grounded component to obstruct the path in which high potential electrons can travel. The dielectric material reduces the potential of the electrons, however, it also significantly impedes the flow of gas. In the case where the bias is of an A/C nature, a faraday cup has been used with limited success.
In view of the foregoing, techniques for effectively increasing the voltage level at which avalanche ionization occurs in low-pressure applications would be desirable.
The present invention is directed to techniques for increasing the voltage level at which avalanche ionization occurs in low-pressure applications. The invention essentially creates a transverse magnetic field across a gas passageway, which reduces the potential energy of charged particles (e.g., electrons) passing through the passageway. The reduction in electron potential energy reduces the energy of collisions between electrons and molecules and therefore reduces the likelihood of avalanche ionization.
One aspect of the invention pertains to a voltage-isolating passageway that includes a passageway and two magnets. The passageway has two openings, each opening configured to be connected to external components and capable of being sealed such that a low pressure environment can be sustained within the passageway. The first and second magnets are positioned along opposite and exterior surfaces of the passageway wherein the first and second magnets impose a magnetic field in a transverse direction with respect to a lengthwise axis of the passageway, the transverse magnetic field tending to reduce the potential energy of charged particles traveling through the passageway. In another aspect of this invention, a semi-conductive material layer that coats an inner surface of the passageway. The semi-conductive material layer is suitable for absorbing at least some of the charged particles that travel through the passageway and conducting their potential safely to ground.
Another aspect of the present invention pertains to a high voltage system having at least two components that are each maintained at different voltage biases. The system includes a vacuum chamber, a vacuum pump, and a voltage isolating passageway. The vacuum chamber is maintained at a very high electrical potential while the vacuum pump is maintained at substantially a ground potential and creates a vacuum within the vacuum chamber. The voltage isolating passageway connects the vacuum chamber and the vacuum pump and includes a passageway and magnets as described in the first aspect of the invention.
These and other features and advantages of the present invention will be presented in more detail in the following specification of the invention and the accompanying figures, which illustrate by way of example the principles of the invention.